1. Field of the Invention
The present invention relates to a low melting point glass containing no lead. Further, it relates to a glass ceramic composition containing a powder of this low melting point glass, which is useful for sealing a cathode ray tube or a flat display panel such as a plasma display panel (PDP) or a vacuum fluorescent display (VFD), for covering a substrate, or for forming partition walls in PDP or VFD.
2. Discussion of Background
Heretofore, a PbO-B2O3-ZnO-SiO2 type crystallizable low melting point glass as disclosed, for example, in JP-B-36-17821, has been used for sealing a panel and a funnel of a cathode ray tube. Such a crystallizable low melting glass is coated on a sealing portion and then maintained at a temperature of from 440 to 450xc2x0 C. for from 30 to 40 minutes, whereby the panel and the funnel will be sealed. The panel and the funnel thus sealed are evacuated while being heated at a temperature of from 300 to 380xc2x0 C. to attain a high degree of vacuum with a pressure of at most 10xe2x88x926 Torr, and then sealed.
Further, heretofore, a low melting point glass has been used also for sealing a glass substrate in PDP or VFD, and it has been sealed at a temperature of from 440 to 500xc2x0 C. In the case of VFD, the panel thus sealed is evacuated while being heated at a temperature of from 250 to 380xc2x0 C. to attain a high degree of vacuum and then sealed. In the case of PDP, the panel is likewise evacuated while being heated at a temperature of from 250 to 380xc2x0 C., and a discharge gas such as Ne, Nexe2x80x94Xe or Hexe2x80x94Xe is sealed in to a level of from 100 to 500 Torr, and then the panel is sealed.
Heretofore, a glass containing lead has been used as a low melting point glass for sealing. Recently, however, a glass containing no lead has been desired.
Further, the low melting point glass which has heretofore been used for sealing, does not match in the expansion coefficient with e.g. a panel or a funnel of a cathode ray tube, or with a glass substrate to be used for PDP or VFD, whereby it has been likely that the sealed glass tends to break. Further, it has happened that due to the heating at the time of evacuation, the low melting point glass at the sealing portion has tended to flow or foam, or the sealing portion has tended to break.
Further, a low melting point glass to be used for sealing, covering or forming partitions walls in PDP or VFD, is required not to contain an alkali metal oxide which is likely to lower the electrical insulating property, or even if it contains such an alkali metal oxide, the content is required to be small. As such a glass, an attention has been drawn to a tin zinc phosphate type glass.
However, a tin zinc phosphate type glass heretofore known, has had the following problems.
(1) Due to the heating at the time of evacuation, the low melting point glass at the sealing portion tends to flow or foam, or the sealing portion tends to break.
(2) The glass is likely to undergo crystallization during firing, and when firing and flowing are carried out twice or more, the glass tends to hardly flow in the second or subsequent firing. Further, the dimensional fluctuation increases with the progress of crystallization by repetition of firing.
It is an object of the present invention to provide a low melting point glass and a glass ceramic composition which solve the above problems.
The present invention provides a low melting point glass (a glass of first embodiment) consisting essentially of, as represented by mol % based on the following oxides:
wherein SnO+ZnO+P2O5+B2O3 is at least 76 mol %, Li2O+Na2O+K2O is from 0 to 9 mol %, MgO+CaO+SrO+BaO is from 0 to 35 mol %, and the molar ratio of SnO to ZnO is less than 1.
Further, the present invention provides a low melting point glass (a glass of second embodiment) consisting essentially of, as represented by mol % based on the following oxides.
wherein Li2O+Na2O+K2O is from 0 to 9 mol %, MgO+CaO+SrO+BaO is from 0 to 30 mol %, and the molar ratio of SnO to ZnO is less than 1.
Still further, the present invention provides a low melting point glass (a glass of third embodiment) consisting essentially of, as represented by mol % based on the following oxides:
wherein Li2O+Na2O+K2O is from 0 to 3 mol %, MgO+CaO+SrO+BaO is from 0 to 35 mol %, Al 2O3+In2O3+WO3 is from 0 to 3 mol % and the molar ratio of SnO to ZnO is less than 1. The glass of third embodiment is effective particularly for solving the above-mentioned problem (2).
Further, the present invention provides a glass ceramic composition containing a powder of the low melting point glass of first, second or third embodiment.
The low melting point glass of the present invention (hereinafter referred to simply as the glass of the present invention) has a softening point Ts of at most 600xc2x0 C. If the softening point exceeds 600xc2x0 C., it tends to be difficult to employ such a glass for sealing, covering or formation of partition walls for e.g. PDP or VFD. The softening point is preferably at most 580xc2x0 C., more preferably at most 560xc2x0 C., most preferably at most 550xc2x0 C.
Further, when the glass is used for covering or formation of partition walls for e.g. PDP or VFD, Ts is preferably at least 500xc2x0 C. If it is less than 500xc2x0 C., the covering or the formation of partition walls tends to be difficult. It is more preferably at least 510xc2x0 C., particularly preferably at least 520xc2x0 C., most preferably at least 530xc2x0 C.
When the glass of the present invention is used for sealing, covering or formation of partition walls, it is usually pulverized for use. Such pulverized glass is mixed with a low expansion ceramic filler, a heat resistant pigment, etc., as the case requires, and then kneaded with a vehicle to obtain a paste. This glass paste is coated at a predetermined portion of a substrate glass and fired. Here, the substrate glass includes one having a transparent conductive film or the like coated on glass.
The crystallization temperature (Tc) of the glass of the present invention is preferably higher by at least 40xc2x0 C. than Ts. if the difference between Tc and Ts, i.e. (Tcxe2x88x92Ts), is less than 50xc2x0 C., the glass tends to be crystallizable during firing. Here, Tc is the crystallization peak temperature obtainable by a differential thermal analysis, and when the crystallization peak is not observed, Tc=∞. (Tcxe2x88x92Ts) is more preferably at least 60xc2x0 C., particularly preferably at least 70xc2x0 C. most preferably at least 80xc2x0 C.
When the glass of the present invention is used for sealing for e.g. a cathode ray tube, PDP or VFD, the average linear expansion coefficient in a range of from 50 to 300xc2x0 C. is preferably at most 120xc3x9710xe2x88x927/xc2x0 C. Hereinafter, the average linear expansion coefficient in a range of from 50 to 300xc2x0 C. is represented by xcex1300.
When the glass of the present invention is used for covering or formation of partition walls for PDP or VFD, the average linear expansion coefficient in a range of from 50 to 250xc2x0 C. is preferably at most 120xc3x9710xe2x88x927/xc2x0 C. If it exceeds 120xc3x9710xe2x88x927/xc2x0 C., matching of the expansion coefficient to the substrate glass tends to be difficult. The average linear expansion coefficient is more preferably at most 110xc3x9710xe2x88x927/xc2x0 C., particularly preferably at most 100xc3x9710xe2x88x927/xc2x0 C. Further, the above linear expansion coefficient is preferably at least 60xc3x9710xe2x88x927/xc2x0 C. Hereinafter, the average linear expansion coefficient in a range of from 50 to 250xc2x0 C., is represented by xcex1250.
Now, the composition of the glass of the present invention will be described below, wherein mol % will be referred to simply as %.
SnO is a component which lowers the softening point to increase the fluidity, and is thus essential. If it is less than 2%, the softening point tends to be too high, whereby the fluidity tends to decrease, and for example, the strength and air tightness of the sealing portion will be impaired, and sealing may not be accomplished at a temperature of from 400 to 600xc2x0 C. It is preferably at least 3%, more preferably at least 7%, still more preferably at least 10%, particularly preferably at least 15%. If it exceeds 37.5%, the meltability of the glass tends to be low, and a coating film-like foreign matter layer is likely to be formed on the surface of molten glass, whereby it tends to be difficult to obtain a homogeneous glass. Preferably, it is at most 35%, more preferably at most 30%, particularly preferably at most 25%.
ZnO is essential and effective for stabilizing the glass, or improving the chemical durability, particularly the water resistance, lowering the expansion coefficient or lowering the softening point. If it is less than 5%, the above effects will be small. It is preferably at least 20%, more preferably at least 24%, particularly preferably at least 25%, most preferably at least 32%. If it exceeds 73%, the softening point tends to be too high, the glass tends to undergo devitrification, or it tends to crystallize during firing. It is preferably at most 71%, more preferably at most 45%, particularly preferably at most 35%, most preferably less than 32%.
When B2O3 is contained, the content of ZnO is preferably from 5 to 45%.
The molar ratio of SnO to ZnO, i.e. the value obtained by dividing the content of SnO by the content of ZnO, must be less than 1. If this molar ratio is 1 or higher, the meltability of the glass deteriorates, and a film-like foreign layer is likely to be formed on the molten glass surface. The molar ratio is preferably at most 0.97, more preferably at most 0.93, particularly preferably at least 0.90, most preferably at most 0.8.
P2O5 is a network former and essential. If it is less than 16%, vitrification tends to be difficult. It is preferably at least 25%, more preferably at least 27%, particularly preferably at least 28%. If it exceeds 50%, the chemical durability, particularly the water resistance, tends to deteriorate. It is preferably at most 40%, more preferably at most 37%.
B2O3 is effective for stabilizing the glass, increasing the fluidity, lowering the expansion coefficient or the like. In the glass of first embodiment and the glass of second embodiment, B2O3 is not essential, but in the glass of third embodiment, B2O3 is essential. If the content of B2O3 exceeds 30%, the softening point tends to be too high, whereby the fluidity deteriorates, and, for example, the strength and air tightness of the sealing portion tend to be impaired, the chemical durability deteriorates, or the glass tends to be unstable. It is preferably at most 20%, more preferably at most 15%, particularly preferably at most 10%, most preferably at most 5%. When B2O3 is contained, its content is preferably at least 0.1%. If it is less than 0.1%, the above-mentioned effects tend to be too small. It is more preferably at least 0.5%, particularly preferably at least 1%. The total of contents of SnO, ZnO, P2O5 and B2O3 is preferably at least 76%. If the total is less than 76%, vitrification tends to be difficult.
Each of Li2O, Na2O and K2O is not essential, but may be contained up to 9% each, in order to increase the fluidity by lowering the softening point. If the content exceeds 9%, the electrical insulating property tends to deteriorate, the chemical durability tends to deteriorate or the expansion coefficient tends to be too large. Each content is more preferably at most 3%, particularly preferably at most 1%, most preferably at most 0.5%. When the electrical insulating property is of importance, it is preferred that none of Li2O, Na2O and K2O is contained substantially i.e. their contents are not higher than impurity levels.
The total of contents of Li2O, Na2O and K2O is at most 9%. If the total content exceeds 9%, the electrical insulating property tends to deteriorate, the chemical durability tends to deteriorate or the expansion coefficient tends to be too large. The total content is more preferably at most 3%, particularly preferably at most 1%, most preferably at most 0.5%.
Al2O3 is not essential, but may be contained up to 20%, as it is effective for lowering the expansion coefficient, increasing the chemical durability or suppressing crystallization during firing. If it exceeds 20%, the softening point tends to be too high, whereby the fluidity deteriorates, and for example, the strength and air tightness of the sealing portion tend to be impaired. It is more preferably at most 10%, particularly preferably at most 5%, most preferably at most 4%. When Al2O3 is contained, its content is preferably at least 0.1%.
SiO2 is not essential, but may be contained up to 20% in order to lower the expansion coefficient. If it exceeds 20%, the softening point tends to be too high, whereby the fluidity deteriorates, and for example, the strength and air tightness of the sealing portion tend to be impaired. It is more preferably at most 10%, particularly preferably at most 5%. In order to lower the softening point, it is preferred not to substantially contain SiO2. If SiO2 is contained, its content is preferably at least 0.1%.
Each of MgO, CaO, SrO and BaO is not essential, but may be contained up to 35% each, in order to stabilize the glass or to suppress crystallization during firing. If the content exceeds 35%, the softening point tends to be too high. It is more preferable at most 30%, particularly preferably at most 19%, most preferably at most 15%.
When at least one member among MgO, CaO, SrO and BaO, is contained, the total content is preferably at most 35%. If the total content exceeds 35%, the softening point tends to be too high. It is preferably at most 30%, more preferably at most 20%, particularly preferably at most 19%, most preferably at most 15%. In a case where it is desired to suppress the crystallization during firing or stabilize the glass, the above-mentioned total content is preferably at least 2%, more preferably at least 2.5%, particularly preferably at least 4%, most preferably at least 8%.
Each of In2O3 and WO3 is not essential, but may be contained up to 10% each, in order to increase the chemical durability or to suppress crystallization during firing. If the content exceeds 10%, the softening point tends to be too high. It is more preferably at most 5%, particularly preferably at most 4%.
When at least one member among Al2O3, In2O3 and WO3, is contained, the total content is preferably at most 10%. If the total content exceeds 10%, the softening point tends to be too high. The total content is more preferably at most 7%, particularly preferably at most 5%. On the other hand, the total content is preferably at least 0.5%.
The glass of the present invention consists essentially of the above-mentioned components, but may contain other components in a total of up to 5 mol %. As such other components, rare earth oxides such as La2O3 and CeO2, TiO2, V2O5, MnO, Fe2O3, CoO, NiO, CuO, Y2O3, ZrO2, MoO3, Rh2O3, PdO, Ag2O, TeO2, and Bi2O3, may, for example, be mentioned. Each of PbO and CdO is not substantially contained, i.e. is not higher than the impurity levels.
Further, it is preferred that a halogen element such as F or Cl is not substantially contained. The halogen atom is likely to gasify during firing and react with a phosphor in PDP, VFD or the like to deteriorate the phosphor or to deposit on a filament of VFD to deteriorate the emission.
Now, a glass ceramic composition and a conductive paste employing the glass of the present invention, will be described. The glass ceramic composition of the present invention contains a powder of the glass of the present invention as an essential component and may further contain a low expansion ceramic filler or the like. Here, the low expansion ceramic filler is a ceramic powder having xcex1300 of at most 70xc3x9710xe2x88x927/xc2x0 C.
When the glass of the present invention is used for sealing a panel and a funnel of a cathode ray tube (hereinafter referred to simply as sealing of a cathode ray tube), the content of the powder of this glass is preferably from 60 to 100 wt %. The low expansion ceramic filler has an effect to reduce the expansion coefficient, whereby matching of the thermal expansion coefficient to the panel and the funnel will be facilitated. If the above-mentioned content of the glass powder is less than 60 wt %, the fluidity tends to be too low, whereby the air tightness of the sealing portion tends to be impaired. It is more preferably from 65 to 99 wt %, particularly preferably from 70 to 99 wt %.
On the other hand, the low expansion ceramic filler is preferably contained within a range of from 0 to 40 wt %, although it is not essential. If the total content of the low expansion ceramic filler exceeds 40 wt %, the fluidity at the time of sealing tends to be low. The total content is more preferably from 1 to 35 wt %, particularly preferably from 1 to 30 wt %.
As such a low expansion ceramic filler, a powder of alumina, mullite, zircon, cordierite, aluminum titanate, xcex2-spodumene, silica, xcex2-quartz solid solution or xcex2-eucryptite is easy to handle and preferred. These fillers may be used alone or in combination as a mixture of two or more of them.
Among low expansion ceramic fillers, the total content of alumina, mullite and zircon is preferably at most 9 wt %. The average linear expansion coefficient in a range of from 50 to 350xc2x0 C. is from 65xc3x9710xe2x88x927 to 75xc3x9710xe2x88x927/xc2x0 C. with alumina, from 50xc3x9710xe2x88x927 to 60xc3x9710xe2x88x927/xc2x0 C. with mullite, and from 42xc3x9710xe2x88x927 to 48xc3x9710xe2x88x927/xc2x0 C. with zircon. Thus, the expansion coefficients are relatively large, and even if they are mixed with the powder of the glass of the present invention, the effects to adjust the expansion coefficient are smaller than other low expansion ceramic fillers. By controlling the content of the low expansion ceramic filler within the above-mentioned preferred range, the desired expansion coefficient can be obtained without substantially reducing the amount of the glass powder, whereby it is possible to improve the strength of the sealing portion. In such a case, at least one member among alumina, mullite and zircon may be contained, or none of them may be contained.
For reference, average linear expansion coefficients (unit: xc3x9710xe2x88x927/xc2x0 C.) in a range of from 50 to 350xc2x0 C. of other low expansion ceramic fillers will be shown below.
It is preferred that xcex1300 of a fired body obtainable by firing a glass ceramic composition to be used for sealing a cathode ray tube is from 80xc3x9710xe2x88x927 to 110xc3x9710xe2x88x927/xc2x0 C. If xcex1300 is outside this range, a tensile stress will be exerted to the panel glass, the funnel glass or the sealing portion, whereby the pressure resistance of a valve having the panel glass and the funnel glass sealed, will deteriorate.
Further, when the glass of the present invention is used for sealing PDP or VFD, the content of a powder of the above glass is preferably from 50 to 100 wt %. If a low expansion ceramic filler is incorporated, it provides an effect to reduce the expansion coefficient, whereby matching of the expansion coefficient to the substrate of PDP or VFD will be facilitated. If the content of the glass powder is less than 50 wt %, the fluidity tends to be poor, and the air tightness of the sealing portion tends to be impaired. The content is more preferably from 55 to 99 wt %, particularly preferably from 60 to 98 wt %.
On the other hand, in such a case, the low expansion ceramic filler is not essential, but is preferably contained in an amount of from 0 to 50 wt %, more preferably from 1 to 45 wt %, particularly preferably from 2 to 40 wt %.
As such a low expansion ceramic filler, like in the case of the sealing composition for a cathode ray tube, a powder of alumina, mullite, zircon, cordierite, aluminum titanate, xcex2-spodumene, silica, xcex2-quartz solid solution or xcex2-eucryptite, is preferred from the viewpoint of handling efficiency. These fillers may be used alone or in combination as a mixture of two or more of them.
Further, among the low expansion ceramic fillers, the total content of alumina, mullite and zircon is preferably at most 9 wt %. In such a case, at least one member among alumina, mullite and zircon may be contained, or none of them may be contained. As mentioned above, alumina, mullite and zircon have relatively large expansion coefficients, and even if they are mixed with the powder of the glass of the present invention, the effect to adjust the expansion coefficient is smaller than other low expansion ceramic fillers. By adjusting the content of the low expansion ceramic filler within the above preferred range, it is possible to obtain the desired expansion coefficient without substantially reducing the amount of the glass powder, and such will be effective for improving the strength of the sealing portion.
It is preferred that xcex1250 of a fired body obtainable by firing a glass ceramic composition to be used for sealing PDP or VFD, is from 60xc3x9710xe2x88x927 to 90xc3x9710xe2x88x927/xc2x0 C. If xcex1250 is outside this range, a tensile stress will be exerted intensively to the substrate glass or the fired body, whereby the strength of the sealing portion is likely to deteriorate.
A heat resistant pigment may be incorporated as a coloring agent to a glass ceramic composition to be used for sealing PDP or VFD, in order to improve the appearance of the display.
Further, when the glass of the present invention is used for coating a substrate, it is preferred that the content of the powder of this glass is adjusted to be from 50 to 100 wt %, and the content of a low expansion ceramic filler is adjusted to be from 0 to 50 wt %, although such a low expansion ceramic filler is not essential. The substrate can be covered by coating such a glass ceramic composition for coating, on the substrate, followed by heating at a temperature of from 400 to 700xc2x0 C. for from 5 minutes to 1 hour. Here, the material for the substrate may, for example, be a heat resistant material such as glass or ceramics. Further, as the low expansion ceramic filler, the one which is the same as for the above-mentioned ceramic composition for sealing, may be employed.
Still further, when the glass of the present invention is used for forming partition walls of PDP or VFD, it is preferred that the content of the powder of this glass is adjusted to be from 50 to 100 wt %, and the content of a low expansion ceramic filler is adjusted to be from 0 to 50 wt %, although such a low expansion ceramic filler is not essential. In addition, a heat resistant pigment such as a white pigment (such as TiO2) or a black pigment (such as a Fe-Mn type pigment, a Fexe2x80x94Coxe2x80x94Cr type pigment or a Fexe2x80x94Mnxe2x80x94Al type pigment) may be incorporated, as the case requires. Further, as the low expansion ceramic filler, the one which is the same as for the above-mentioned ceramic composition for sealing, may be employed.
The glass ceramic composition of the present invention is usually kneaded with a resin component such as ethyl cellulose, nitro cellulose, an acrylic resin, a poly xcex1-methylstyrene resin or a butyral resin, or with an organic vehicle containing a suitable solvent such as xcex1-terpineol, isoamyl acetate, 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate, phenoxyethanol, ethyl cellosolve, dibutyl cellosolve, dibutyl carbitol, butyl carbitol acetate, or ethylene glycol monophenyl ether, to form a paste for use.
Further, a powder of the glass of the present invention can be used also as a binder for e.g. a conductive paste, a resistive paste or a dielectric paste. For example, when it is used as a binder for a conductive paste, it is preferred to form it into a glass ceramic composition comprising from 1 to 50 wt % of a powder of the glass of the present invention, from 50 to 90 wt % of a conductive powder, and as an optional component, from 0 to 10 wt % of a low expansion ceramic filler powder.
To use such a composition as a conductive paste, an organic vehicle is optionally added to form a paste. Here, as the conductive powder, a powder having electrical conductivity, such as Ag, Pd, Al, Ni, Cu, Au or a mixture thereof, may, for example, be mentioned. By heating and firing such a conductive paste at a temperature of from 400 to 900xc2x0 C. for from 5 minutes to 1 hour, a conductive body can be formed.
Now, the present invention will be described in further detail with reference to Examples. However, it should be understood that the present invention is by no means restricted to such specific Examples.
Glass powders having compositions shown in Tables 1 to 3, as represented by mol % in lines for from SnO to SnO/ZnO, were prepared as follows.
85% orthophosphoric acid was dropwise added to solid starting materials other than P2O5, to obtain a starting material slurry, which was thoroughly mixed and then dried at 120xc2x0 C. to obtain a powder batch. This powder batch was put into a quartz crucible and after covered with a lid, melted (typically melted for 30 minutes) at a temperature of from 900 to 1,200xc2x0 C. (typically at 1,100xc2x0 C.) and then formed into a flake-shaped glass by water granulation or by passing through stainless steel rollers. Then, the flake-shaped glass was pulverized in an alumina ball mill for a predetermined period of time (typically for 105 minutes) to prepare a glass powder.
With respect to some glasses in Tables 1 to 3, the softening point Ts and the expansion coefficient xcex1G were measured, and the results are shown in the Tables.
Ts (unit: xc2x0 C.): Using a glass powder having an average particle size of from 10 to 20 xcexcm, Ts was measured by raising the temperature from room temperature to 800xc2x0 C. at a temperature raising rate of 10xc2x0 C./min by a differential thermal analysis. Here, an alumina powder was used as a standard substance.
xcex1G (unit: xc3x9710xe2x88x927/xc2x0 C.): The above-mentioned molten glass was cast on a stainless steel plate and slowly cooled in the vicinity of the glass transition point. The cooled glass was formed into a rod having a diameter of 2 mm and a length of 20 mm, which was used as a sample, and using quartz glass as a standard sample, the elongation was measured under a condition of a temperature raising rate of 10xc2x0 C./min by a differential thermal expansion meter. With respect to glasses for a cathode ray tube in Tables 1 and 2, the average linear expansion coefficients were calculated in a range of from 50 to 300xc2x0 C., and with respect to the glasses for other applications in Tables 1 and 2 and the glasses in Table 3, the average linear expansion coefficients were calculated in a range of from 50 to 250xc2x0 C., and they were taken as xcex1G, respectively.
The glass powder and the low expansion ceramic filler in Table 1 were mixed in a ratio as represented by wt % in the lines for xe2x80x9cGlassxe2x80x9d and xe2x80x9cFillerxe2x80x9d in xe2x80x9cConstructionxe2x80x9d in Table 1, to prepare a glass ceramic composition. Here, Examples 1 to 8 represent Working Examples of the present invention, and Examples 9 and 10 represent Comparative Examples. The glass of Example 11 is a glass of the present invention, but the glass ceramic composition of Example 11 is outside the scope of the present invention. With respect to this glass ceramic composition, the flow button diameter, the residual strain and the expansion coefficient were measured, and the results are shown in Table 1.
Flow button diameter (unit: mm): The flow button diameter indicates the fluidity of the glass ceramic composition during sealing. Firstly, a sample powder of the glass ceramic composition is prepared in an amount of 5.5 g with respect to one for a cathode ray tube or 3.5 g with respect to one for PDP or VFD. Then, this sample powder is press-molded into a cylindrical shape having a diameter of 12.7 mm and then held at a firing temperature (unit: xc2x0 C.) as identified in Table 1 for 30 minutes for firing. The diameter of the fired body obtainable by the firing is taken as the flow button diameter. This flow button diameter is desired to be at least 26.5 mm with respect to a glass ceramic composition for sealing a cathode ray tube, or at least 20.0 mm with respect to a glass ceramic composition for sealing PDP or VFD.
Residual strain (unit: nm/cm): A glass ceramic composition and an organic vehicle (a solution having 1.2% of nitrocellulose dissolved in isoamyl acetate) are mixed in a weight ratio of 6.5:1 to obtain a glass paste. In the case for a cathode ray tube, this glass paste is coated on a funnel glass specimen, and in the case for sealing PDP or VFD, this glass paste is coated on a substrate glass specimen, followed by firing under the same condition as in the case for the flow button diameter. The residual strain (unit: nm/cm) formed between the funnel glass specimen or the substrate glass specimen, is measured by a polarimeter. The symbol xe2x80x9c+xe2x80x9d in the Table represents a case where the above fired body receives a compression strain, and the symbol xe2x80x9cxe2x88x92xe2x80x9d represents a case where the fired body receives a tensile strain. This residual strain is desired to be within a range of from xe2x88x92100 to +500 nm/cm.
Expansion coefficient (unit: xc3x9710xe2x88x927/xc2x0 C.) : A glass ceramic composition is fired under the same condition as in the case for the flow button diameter and then polished into a desired size, whereupon the elongation is measured under a condition of a temperature raising rate of 10xc2x0 C./min by a differential thermal expansion meter. With respect to one for sealing a cathode ray tube, the average linear expansion coefficient is calculated in a range of from 50 to 300xc2x0 C., and with respect to one for sealing PDP or VFD, the average linear expansion coefficient is calculated in a range of from 50 to 250xc2x0 C. (for PDP). Taking into consideration the matching to the expansion coefficient of the object to be sealed, the average linear expansion coefficient is desired to be from 80xc3x9710xe2x88x927 to 110xc3x9710xe2x88x927/xc2x0 C. with respect to one for a cathode ray tube, or from 60xc3x9710xe2x88x927 to 90xc3x9710xe2x88x927/xc2x0 C. with respect to one for sealing PDP or VFD.
One of the glass ceramic compositions of Examples 1 to 5 and 9 was placed between a funnel and a panel for 25 model and held at a temperature of from 400 to 500xc2x0 C. for 30 minutes to seal the funnel and the panel thereby to obtain a bulb. On the other hand, one of the glass ceramic compositions of Examples 6, 7 and 10 was coated along edges of PDP substrates having electrodes and partition walls preliminarily formed, and held at a temperature of from 400 to 600xc2x0 C. for 30 minutes for sealing to obtain PDP. Further, a grid was placed between the edges of glass substrates having electrodes, etc. formed, and one of the glass ceramic compositions of Examples 8 and 11 was placed along the edges and held at a temperature of from 400 to 600xc2x0 C. for 30 minutes to seal the glass substrates to each other to obtain VFD. With respect to such bulb, PDP and VFD, the strength under water pressure and the strength in high temperature were measured as follows. The results are shown in Table 1.
Strength under water pressure (unit: kgf/cm2): A pressure difference is exerted by water between the interior and the exterior of the bulb, PDP or VFD, and the pressure difference at breakage is measured. Such measurement is repeated five times, and the average value is taken as the strength under water pressure. To guarantee the strength of the bulb, PDP or VFD, this strength under water pressure is desired to be at least 3 kgf/cm2.
Strength in high temperature (unit: xc2x0 C.): A temperature difference is exerted by water and hot water between the interior and the exterior of the bulb, PDP or VFD, and the temperature difference at breakage is measured. The measurement is repeated five times, and the average value is taken as the strength in high temperature. In view of the thermal stress formed in the heat treatment step in the production of a cathode ray tube, PDP or VFD, this strength in high temperature is desired to be at least 45xc2x0 C.